@Mooregrow welcome to the forum
@St. Tom thanks for the tag
I'll try and look at as many contributing factors as I can, some solutions may cost some money, some may not.
If you have to fork out some cash, look at it as an investment. Once an issue has been addressed, it should last for years.
I will add a synopsis at the end for quick and convenient info.
Standing water will evaporate in a warm tent. I use a wet/dry vacuum to suck up my run off! It is quick and easy.
I had a quick look and in the US you can pick one up from around $70. Maybe even cheaper if you have a look around, I don't live in the USA.
In the UK I picked one up for £44 for my wet/dry vac (I wouldn't be without it with Drain To Waste (DTW) in coco)
Do you know what the RH is outside of the tent? I live in a high RH area so RH is relatively high for me compared with people who leave in the east of my country.If you have high RH outside the tent, you could run a dehumidifier to dehumidify the air before it goes in the tent.
Reducing the temp - if this is possible, it will help, as hot air holds more moisture than cool air.
Insulating the tent in cold weather is also a good idea.
A thermostatic tube heater is a good way to keep temps at an ideal heat in winter but if your not getting enough heat, then your heater isn't big enough.
You may find the heater you have is sufficient once tent is insulated. If you still can;t keep the heat up after insulating, you will need to add another tube heater. Luckily they don't take up much space.
Lollypopping your plants will allow more air to circulate below the canopy.
Any foliage low down, that doesn't get decent light penetration, can be removed.
It is waste of time letting the larf/popcorn buds grow.
You can use clay pebbles as a mulch on the surface of your substrate, to stop excessive moisture loss from you pots.
However I think you humidity problems is fro the plans transpiring.
Synopsis
In hot weather
Reduce the number of plants in the tent - less plants equals less transpiration and gives more space for air to move around your tent
We all want to grow as many plants as we can but pushing the limits of your grow space can lead to problems.
Reduce heat- less moisture held in the air and plants transpire less moisture.
Dehumidify air going into tent - take out moisture before it goes in the tent.
Clay pebble mulch - stops evaporation from the top of your pots.
Possibly change from fabric pots to solid pots - less moist surface area on the sides of the pots from which moisture can evaporate.
Remove standing water, with a wet/dry vac - in a hot tent the standing water
will evaporate creating a higher RH.
Have a wet/dry, water/feed cycle - cannabis likes a wet/dry cycle and you will also reduce the amount of times you need to water.
A wet/dry cycle allows the ph to fluctuate a little giving better nutrient take up and allowing more air to the roots.
Remove unnecessary foliage low down on the plant - by lollypopping, helps, air flow and there is less foliage to transpire moisture.
In cold weather
Insulate tent- The tube heater you have, may then be right size and provide enough heat.
Polyisocyanurate (PIR) insulation board is relatively cheap, I believe Cellotex is available in the USA
If heat still isn't enough- add another tube heater (thermostatic controlled)
I hope that helps answer your questions
Have a great day and an even better grow
Arty