First Version
A couple of years ago now we purchased a SeeLevel system for our 26ft trailer, well because the tank monitors were screwing up even before we started filling our tanks. That install was pretty straightforward as things around RVs go. All three tanks were transverse in the front half of the trailer. All the factory monitors and thus wires were on the same side. The sides of the tanks were flat so placing the sensors was easy. SeeLevel II reuses the existing wiring so that wasn’t a problem either. Inside the trailer – the factory level gauge was in the upper left corner of the main control panel and there was sufficient room that I was able to cut out the factory junk and then insert the SeeLevel panel right into the hole over the panel.
Second Version
So eventually, we traded in our TT for a Class C; Forest River, Sunseeker 3050S. You might think with a bigger vehicle, it might be easier to get the guts and work on things. Nope – no way, nada, can’t do it! Well, it won’t be easy.
The first clue was that the fresh water fill was 6 feet up on the right side. Huh? In the bedroom – there is a closet that runs the length of the right side of the RV. It stops 2 feet or so above the floor. The fresh water tank is in that space. If you take out the closet floor (don’t), you can see the top of the tank. If you go into the rear basement storage and take out the front wall – you can access the tank monitor, the fill, the overflow and the tank outlet hoses. So that is the only access to the fresh water, big enough to place the SeeLevel components. More on this later.
The black and grey tanks run transverse, under the floor, just forward of that area.
Both ends can be accessed by taking down the plastic panels in the storage bins just behind the rear wheels. The tanks have a sloping bottom. They are about 5 inches thick on the right side and 8 on the left side. So the factory tank monitors are on the left side – as are the actual drains. My grey tank doesn’t vent right but that is a story for another post.
Tight Spaces
The black tank is forward of the grey – and only the back half of it is really accessible. AND – there is a step built into the end of the tanks so they can use a metal bracket to mount them to the floor. This leaves only the sides for attaching the SeeLevel sensors. Maybe you see where this is going. The only side accessible on the black tank was the one 1” or less from the grey tank. To add insult to injury – they placed the tank heaters on the end of the tank. These are some sort of wire grid, backed by 3/16 sticky foam about 8 inches wide and long enough to wrap around ¾ of the tank. So now my only accessible place to mount the sensors to the black tank as between the tanks and about a foot deep into that space.
As I was concerned about the sensors working in tight space, I contacted SeeLevel (Garnet) and they suggested shielding the sensors with 1/16 rubber gasket material. Ok – so I actually used that on all three sensors because I had no idea what might be pushed up against the wall in the basement storage area.
But how to do this. Each SeeLevel Sensor is a flexible printed circuit – with components right oh the surface and a very sticky glue on the back. I knew I was only going to get one chance to get this installed. Any “second chance” was going to cost me another sensor. (first I stuck a folded paper towel to a paint stir stick, applied rubbing alcohol liberally – and used that to clean the side of the tank. Yes, I have alcohol wipes, but this was no place to mess around with little pieces of alcohol dipped paper.
The freshwater sensors went in first, and easiest, as access was quite open. Then I took the paper that came off the fresh water tank sensors and taped it to the top of the paper protecting the back of the black tank sensor. Then I took a long stick and taped it to the front of the sensor with gaffer’s tape – taking care to only place the tape on the edges away from components.
I was able then to slide the monitor strip between the tanks and hold it in place while I pulled down on the paper to uncover the glue on the back of the strip. The stick was able to put enough pressure on the strip to stick it in place. Then I took another paint stick – added a couple of the pieces of rubber gasket and taped over. I then used this stick – while carefully looking down the gap between tanks – to press the strip to the tank. This took a while as I didn’t want to pull off any of the components in the process. 
Now for the rubber gasket shield. Same process, different parts. I cut a piece of the gasket material that was about 3 inches wider than the strip. Down both edges on one side, I applied a heavy duty double stick (outdoor) tape, leaving the plastic strip on the one side. I then attached plastic and some leftover rubber strips to the cover plastic so I could pull it down in the same fashion as I did the monitor strip.
I pulled the rubber sheet up alongside the monitor strip. I couldn’t tell very well if I had the horizontal placement correct looking from the end, so I put my phone, in camera mode, under the two tanks, looking up – and used that to try to make sure the monitor strip was in between the 
double stick tape attached to the rubber. When I thought all was lined up – I pulled down on each of the tape covers and pushed the sheet against the tank. Then I worked my stick back and forth until the tape let go of the sheet. Then I used the paint stick with rubber on it to push on the gasket to make sure the double stick tape was making good contact.
Next, I cut the old sensor wires and hooked up the new ones. I almost forgot the SeeLevel monitors come with about 8 inches of wire – which often is long enough. For these grey and black tanks, I had added another 18 inches to make connecting a bit easier. It was absolutely required for the black tank.
Inside – there was no room to cut the monitor panel into the existing panel – and some generator indicators were part of the tank monitor and I wanted to leave those for now. Thus I cut a space for the SeeLevel monitor below my existing panel.
Ok, now for my Forest River rant.
When working on the panel – I needed to remove two wires from their spade lugs – did I say that? Actually, I needed to pull two spade lugs from the back of a switch so I could add power and ground for the SeeLevel. The wires pulled right out of the spade lugs – as I expect, many of the wires on the panel would do. Forest River cannot reliably put terminals and crimps on their wires!!! I’ve seen this problem dozens of times on RVs I’ve worked on. All too often crimp connectors are installed with PLIERS! Never use pliers – use a real crimp tool.
Second – look at this panel that covers the fresh tank. There were 5 screw holes UNDER the trim meaning someone put it together that way – THEN decided trim was necessary because it looks like they cut the wall panel with a chainsaw. Of course, the trim was nailed in. When I went to reinstall it all, I put screws in because I might just need to get back into that space. Why use 10 screws on three sides of the panel, then a dozen nails on one side with trim?
I’m a happy user of SeeLevel II. I just recommend if you want to install yourself, step one is exploring your tanks to make sure you can find a place to install them. Measure your flat space because you’ll need that to order your sensors.