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While I may be new to hot tubs, I have been a licensed pest control operator for years. The carpenter ants around the cover are not necessarily a sign that they are nesting in the cabinet, but it is a very real possibility. Ants look for three things, for the most part. Food. Water. Shelter. Heat is not something they seek out usually. Your hot tub provides two out of three. Water and shelter. Under the cover is a water source. The foam and wood in the cabinet is shelter and maybe water, too. BTW, ants don't eat wood or foam for food, but will build nests in it. You will never keep all the ants off the tub. You can, however, have your pro treat around the tub area with either Phantom or Termidor. Both are professional grade pesticides with fipronil as the active ingredient. Both are excellent at controlling ants. You should also spend some time trying to follow ants to their nests-usually trees or damp wood. Put the kids on tracking duty. Kill the nests when you find them. Ants regularly go over 100 feet from the nest. Good luck.