Thank for comments guys!
Sewers - yeah they are a bit out of place! Too Italian I think and not grungy enough. Main thing was to get the shape in, and basic idea. Will fix them later on once map has been given a first pass.
RA7 - nah not breakable trailers, but I think some will have to look a bit broken so that there is some variety. Otherwise, they will look too similar. Also, thanks for reference image and Lanmaniax pimp (great to see it back!).
blackdog - yeah the flatness and the fact that trailers are low has limited what can be done. I did find some raised trailer references, but they looked kind of ridiculous in the map (see below). In the end, I have to go with things like steps - (purple trailer and the swimming pool). In the end, the map has similar heights to maps like de_st_marc and dod_flash for example.
Initially I was put off by the lack of height, so blocked out another map - de_hydro or something similar based in a dam, but made sure it had loads of height variation. However, I returned to the trailer map because I prefer the theme.