You need not dry with the plant/buds hanging exposed within a tent. As you've seen, drying can happen too fast this way.
Paper bags, boxes with some holes punched in them (I use free boxes from Postal Service or Fedex), putting buds in Grove or other gas-permeable bags or other partially vented container, etc. at suitable temperature in a room/space that has rH equal to or lower than your target value all work for drying over a multi-day period. For ex., put buds in paper bags, put these in your tent and follow drying progress.
And regarding your troubles controlling rH in your tent, why bother? It will be much easier to control the environment in the 'lung' room containing the tent (or is this what you are already doing)?