Change the substrate to moist coconut coir. Holds moisture longer and will not mold. Also put a top on the enclosure. You can cut holes for the light and heat.
You may need to put a liner in the table that way you can keep the substrate moist, and you can use heat cables to heat the water in the substrate to create humidity. You and also get a warm mist humidifier. You also may need to partially cover the enclosure to hold in the humidity...
Richie, I have built and then unbuilt enclosures so many times, I can't even remember them all. Its just kind of a part of tortoise keeping that you must think and rethink things all the time. It is very difficult to keep humidity up in an open enclosure like that. I'll list some things that will help, but the best solution is to humidify the whole room or build a closed chamber.
You can:
Use a humid hide box.
Spray the tortoise and substrate several times a day.
Dump water into the substrate.
Use a big shallow water bowl or two.
Cover the top somehow.
Don't forget that you must not let them get cold with all the moisture and humidity, even at night.
thanx Tom.. feel like building a whole new home for them.. but gotta think it thru.. thanx again.. for now ill spray with warm water intill i build them a new home
I have about 3 inches of topsoil and 2 inches of coco coir and I have no problem with humidity. I spray a whole 20 oz bottle of water on it every other day and it seems to be fine and that is with a 100 Watt heat lamp and an open top.
I should also mention that my enclosure is only 2x3 feet big