As Ann Landers would have said, "kwityerbellyaching"
Just finished redoing my roof. Before I finished the 5 gal. bucket was full of mud dabber nests.
Probably my fault though, after I built the house it took me, ah, a few years to put the soffits on.
Made an easy path and a good home for them.
I've never found any on trailers etc. Just lucky I guess.