Every year we take out our trailer for a trip of about 10 weeks. We have friends that come to the house once a week to add trichlor tabs to our swimming pool and check water chemistry parameters and adjust as necessary. For our spa, in prior years I have tried to use the spa frog bromine/mineral cartridge system. I put in a fresh mineral cartridge and bromine cartridge and ask my friends to change the bromine cartridge once per month. The water has never been very good upon return with this method. I normally time my drain/refill schedule so that I need a drain/refill right when we return from our trip. But I don't want to allow anything funky to get started in the tub while we are gone. Our normal sanitation system is dichlor/bleach because I use the tub everyday and have no problems keeping on top of things.
So what I am looking for is a cheap and easy to administer sanitation system for a 380 gallon tub that is going to be sitting with 100+ degree water but not being used for 10 weeks. We live in the Phoenix area, so even with the tub temp set way down the water will still be hot due to our hot summer temps. I have a few spa frog bromine and mineral cartridges left on hand and would like to use them up, but that is not a high priority if some other system is simple and easy for my friends to manage.
Of course, I could just drain the tub and let it sit empty but I have read that is not a good idea due to drying seals, etc.
Thanks for any guidance.