Thanks for the warning and the fix, Rae!
The best thing you can do is go over your trailer/moho with a fine-toothed comb to find any openings. The larger ones (furnace vent, fridge vent, etc.) can be covered with mesh screen, either over the opening itself or in the door. If on the door, make sure you don't have gaps between the door and the body where something can get in.
If you have small openings (missing rivets, etc.) you will need to fix/fill them properly. Put a rivet back where one is missing. Ants can easily get into those holes. There was a thread on here the other day about blocking other openings-- I think the consensus was to use aluminum wool (like steel wool but made out of aluminum) so as not to cause different-metal corrosion. Gaps can be sealed properly with vulkem or other sealant (PLEASE don't use silicon caulk!).
Bugs are a nightmare down here in the South, but I had no idea you had dirt daubers in Ontario! I was only a kid when I lived there (Sarnia), so I don't really remember bugs.