So I have an update on this problem. Recently, the spiders have come back, even though there is water in the black & gray tanks.
I had been reading a thread about how to quiet a pump using insulation, and our pump is loud, so I thought, sure, lets find the pump, and see what's up. Well, I thought the pump was under the back sink, there is a panel there that had to be unscrewed. So I take 2 screws off at the top and peek in, looking for the pump. What do I find? Not the pump, but more then 10 spider nests, each about the size of your thumb tip!! So I get the vacuum out (brought the Kirby from the house, I didn't want to miss any), vac up all the webs, and nests, never did see 1 spider of any size though. As I cleaned it all up, I noticed a pluming pipe, I believe it's a gray water pipe going through the floor, and it's just open all around it. At least 1/2 inch worth, and I believe this is just open to the underside of the camper, so it may be my entry point. Bought some foam sealer, and will get that sealed up tomorrow.
While I was at it, I also took the access panel off by the tub, mainly looking for spiders. Didn't find any, but I did find a few webs. Vacuumed that area up too.
Finally, I checked the panel under the fridge, BINGO water pump! Noticed there, that they did use the spray foam, to seal up one big hole, but there were 2 other small areas that they used some kind of black foam? Well this has come loose, and no longer plugs up the holes, so I'll spray foam them too. When I'm done with all of that, I'll put the pipe insulation in the lines, and see if it makes the area quieter.
Anyway, just wanted to share all this because I'm sure not everyone would even know they should check these areas for openings.
2013 f150 Ecoboost 4x4
2009 Gray Wolf, 22BH