First off, purchase a new mattress. Nothing more nasty than sleeping on a mattress that somebody else used. Pay the price, go to any place that sells a mattress and get a new one.
Meanwhile, remove the old mattress and "bomb away".
Repeat the "bomb away" in 10-12 days so any eggs that might have been hatched, new bugs will be killed before they mature and can reproduce.
WARNING! You're likely to get posts warning about bug bombing inside the camper and possible explosion! That's a bunch of hog wash! You'd have set off something like 300 thousand bug bombs all at the same time to cause an explosion! I think Myth Buster on television debunked the bug bomb exploding house theory a long time ago.
Set of one bomb at the front of the camper and one at the back. In 30 minutes the mist will be gone. Do nothing. In a few days repeat. After the second bombing, wipe off counters and any surfaces you touch. Vacuum the carpet and you're good to go.
Repeat in a year.
We bug bomb at least once every year with this process, mostly in the middle of the summer to keep fleas at bay!