Most "four season" trailers have R-14 in the walls and R-20 or better in the roof and floor. This is often augmented with Reflectix to give the roof a stated insulation value of R-30 or better. Reflectix really isn't insulation as it only reflects radiant heat but is often touted as such in advertisments.
R-7 is about average for a vacation quality trailer. I have a R-7 insulated trailer in Pahrump and with a single air conditioner it's OK up to about 90 in the summer. Above that the interior temperature climbs accordingly. I haven't had it much below freezing yet.
Most of your heat gain/loss will be through windows and the slideouts. Unless you have a heavily insulated trailer your windows will be single pane glass which transmits a lot of heat. Most slideouts have little or on insulation in their ceilings or floors, especially if it's a flat floor slideout where there isn't a lot of room for insulation.
