Did not read all the replies, but some good responses. Overwhelming response was don't loan out your gear. But not everyone addressed how to refuse without sounding like a d#ck. So here are couple of suggestions (and props to those who may have already mentioned these ideas):
1) Assuming you let them use your old rig (which is at a different location):
They need to come pick it up and return it on specific date(s). When you tell your singer they can use it, up front also tell him they can pick it up on this date(s) and you need it back by this date NO later. You can make up excuse that you need it for rehearsal, other gig, renting it out or even loaning out to other friend. The point is you need it back by a certain date. The point is to give them a deadline to accommodate your schedule since you are doing THEM a favor. When you give people carte blance, they tend to undervalue what you are doing for them. When you put boundaries on it, people start to value it.
Example, if your friend says "hey can you pick up my dry cleaning for me?" (which he should just do himself). If you reply "anytime, no problem", then he will place little value on it. However, if you reply "I have to work late tonight and then get to rehearsal, but I can try to do it after I get off work if it will really help you." You are not being a d#ck since you are still offering to do the favor, but he will realize and value the sacrifice you are making to help him out.
The second point of the deadline to return, is if they are not respectful enough to accommodate your schedule when you are doing them a huge favor, it gives you an out for next time they try to mooch. Next time they try to mooch, you can say "hey guys last time I loaned you the gear, I needed it back on Fri and you guys brought it back a week late. Sorry, can't loan it out to you this time."
2) Assuming you let them use either your old or new rig:
Before you offer the gear, talk face to face with your singer and ask him who is responsible for the gear if it gets damaged, stolen, etc? Your singer will probably throw some BS at you like Jerry (the other band bass player) will cover it and don't worry he is good for it. When he says that, then ask him to ask Jerry for a fully refundable deposit (for the full replacement cost of the rig or equiv price of used gear). Since Jerry is good for it, it should be no problem with Jerry funding the deposit. You are okay with Jerry using your gear but you need a deposit. It is FULLY refundable as long as the gear comes back in same condition as it left. You can point out that you are not even charging a rental fee and letting them use the gear for free (since you are such a nice guy), but you need some security because what happens if the gear gets damaged or stolen while out of your possession? You can also explain that you need a deposit because if something does happen, you don't want to have to play collection agency and chase down funds from people.
In both of the scenarios above you don't look like a d^ck because you are agreeing to do them a favor, but have a small, reasonable request on your side. Either a) they will not be able to meet your reasonable request, so you don't have to loan out your gear or b) they will be able to meet your request and at least you will be covered if the gear gets damaged.
Overall, be confident and firm. If you waiver or sound guilty, then they will think they are right and you are wrong. But if you are firm and believe in what you are saying (i.e. you truly believe it is fair for you to ask for deposit in exchange for letting your gear walk out the door), then they will believe it too.
Congrats on your new rig. Nice gear. Let us know how it goes.
