Even easier
find out where they are going in and out, it's normally a small hole. If it's much bigger than 1", duct tape it so that it's smaller. Fire up a shop vac, hold the nozzle next to the hole. Start beating on the side of your hot tub, get them good and angry, and when they come swarming out they get sucked into a hose at 100 miles per hour, then they smack the container of your shop vac. Most of them will die when they hit the shop vac. This works well, I've done it a couple of times.
Just stand still in case some return from outside, they will first go to the hole to check things out. Then you just suck them up.
Last thing you do is turn off the shop vac, as the blower is spooling down shoot some Wasp killer in the hose, and tape it shut. Let it sit a couple of hours, repeat. Remember they cant get out the discharge due to the filter.
After you stop seeing the buggers come out (ten fifteen minutes or so) and you've got them gassed and taped in your shop vac then remove your panel and shoot the nest. Make sure you remove the next because the larvae will hatch in a couple of days then you start all over again.