Given your weight and the type of riding you do, even those cheap rims should stand up without needing to be trued all the time.

My guess is low tension in the first place; IMO you should start learning how to use a spoke wrench, since you can do everything else... there are plenty of how-tos on the web - check out Sheldon Brown's site or a start.

Try adding a half-turn of tension to each spoke (flip the wheel to check you haven't put the dish out), or maybe a full turn if they're really loose.

Get a feel for good tension by giving the spokes a squeeze on good wheels (around the same spoke count).

Once you have enough tension, your spokes shouldn't unwind due to the friction.