I have several ryobi cordless 18v glue guns... the cheaper version only has one temp, and it gets too hot and often winds up melting foamboard, so I don't use that one for planes very often, but it comes in handy around the house for other things + in the woodshop. I also have many of the ryobi 18v dual temp units, and on the low setting it's perfect for assembling foamboard. I think I have 5 of them, so when I do free build days at the club for little glider planes, it is much easier for everyone to have access to glue guns. I also have several of the RMRC hot glue guns - they're super cheap and run on 3 cell batteries and the smaller glue sticks. With the RMRC guns, you do have to be careful as they have no low voltage protection - you have to periodically check the voltage of the batteries... they do last surprisingly long though on a 2200mah cell, plenty long to build something like a tiny trainer.
Remember when buying glue that there are two sizes... one is about 1/4 inch in diameter, and the other is closer to 1/2 inch. In either case, try to buy the longer glue sticks - I buy gorilla glue 1/4 sticks that are 8 inches long, and I buy adtech brand for the bigger sticks that are 10 inches long. The longer sticks of glue really help with not having to add a new stick at a critical point in the build.