I haven't replaced the tail lights on my RV because it came with LED's but I did replace all of the lights on my big trailer, tail, clearance and backup. One of the reason's they cost more is due to the way they are built, which is much better and more sophisticated (typically) than your incandescent bulb fixture. They will out last the originals at least 5 to one, use less electric and in my case, they are much brighter. You can buy submersible or water proof. I have not had any trailer light issues (other than self inflicted) since I installed the LED's on the trailer and that is probably going on 8 maybe 10 years ago now. IMO, they were worth the extra cost.
Just my 2 cents worth. Good luck