Used a piece of cardboard and made a template to fit the front into truck window and taped it in place with painters tape. Closed off sinks traps, stove vent, AC, and bathroom vent with Glad Press and Seal. Taped the outside with blue 3M painters tape if it didn't stink good, but mostly it worked fine.
Used kid's bubble solution to paint all over seams. Found one huge leak on cabover seam and, surprisingly, all other seams were fine. But it was so easy to do that we are probably just going to leak test it twice a year as part of close down and again in the spring :)
We found that it worked best if you carefully painted the seam and had someone else ready to snap a picture, and then move on. The first bubble that got made was the largest and then it was hard to duplicate to show someone else.... but that may have been due to our cheap bubble solution.