In regards to someone who is looking to rent out their trailer, as the OP is, I say go for it. If it helps make owning it more affordable, why not. Just make sure you have good documents to cover the deal with detail on how damage would be covered, and have good insurance in place. AND, don't forget to charge enough. Maybe check out to see what some of the rental companies charge.
I have done major amounts of business with friends and family, from bathrooms, to basements, kitchens, large scale additions, to a couple new homes. Only in one case did the resultant end in a strained relation, which took a few years to mend. What I like about doing work for them comes from the fact they trust me, and that I will do a good job, and be fair. They also realize it is an occupation for me, and that I need to make money at it.
Personally, I would never consider renting my trailer (or anything I own personally), but would lend it out to a friend or family member in a heartbeat, and have done so. They realize the 'You break it, you fix it' rule. The main reason for not renting it for me would be the hassle involved, as my time right now, what with being super busy with work, is quite precious.
I also do business with my two brothers, owning some rec property, and a few revenue properties together, and there is ZERO question on trust in any dealings any one of us should do on our own, while representing each other. I just sold a property a short while ago while one brother was out of the country on vacation. He just did up power of attorney for me. When I made a deal, I sent him a text with just the selling price, got a response that said "Sounds good, go for it", and sent a reply saying "That was not a question!". The reply back was a smilie face.
I do understand the concerns some of you may have, and have seen first hand with others how this sort of thing can go wrong. I know families that live within a short distance of each other, yet are lucky to get together a few times a year. For us, it is a very regular thing. It all comes down to how sound your relationships are, I think.