If it's a new trailer, chances are the overhead lights are all "permanently installed" LED's. Most are not changeable and if they fail, you replace the entire light assembly. Any incandescent bulbs that might be in the trailer, typically the range hood and possibly reading lights would be 921 "push in" incandescent bulbs. On the outside, it's anybody's guess whether you have LED running lights or incandescent lights, so take a cover off one of the fixtures and see what's in them. Tail/turn signal lights are 1157 incandescent bulbs on most (not all) of Keystone's trailers.
This is one area where things change from model to model, brand to brand and year to year, so what any of us have may not be what you find on your trailer. Nothing is more frustrating than to read about it, go buy what someone suggests and then, in the middle of a camping trip, find that what you bought doesn't fit anything in your trailer, so I'd suggest you do an inventory of what you have and buy replacements for what you see in your RV.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS