Definitely bolt it down. Many of the small safes are fairly easy to open by physically jostling the entire safe; bolting it down makes that harder. I'd suggest locating it someplace where it's reasonably convenient to access; whether in plain sight or not probably doesn't matter too much, though I would probably not have it directly across from the front door or anything like that.
I installed mine in the base for the bed, in a corner that wasn't taken up with the fresh water tank, water pump, and other RV systems. It's a handy place to keep important papers and chocolate reserved for s'mores and similar valuables. I don't have any delusions that my little safe is at all secure against most any criminal who would really want to get in; but it is sufficient against casual thievery.