Then I would suggest snow chains.
I have seen that track go from wiping mud off the visor, to perfect, to so dusty you can’t see in a matter of 8 laps.
I can’t tell you what to do for tires since we never really got a hold of the track ourselves, but maybe below will help others understand the track.
It’s been a year or two since I have been down there, but like you said, the track usually has a layer of loose dirt/dust/sand over a packed layer. It doesn’t have any grip, doesn’t take rubber, not even a prep groove. They mostly run on Sunday afternoon, so they cannot keep moisture in it. It just dries out too quick. It’s not really a coarse sand, but more of a soft powdery dust. The base will pack, but I’m not sure it is what most people would consider hard in other areas of the country. I’ve heard of people determining how hard a track is by seeing how far you can stick a screwdriver in the dirt. Most tracks around here you would be lucky if the handle stopped it from going in. I doubt you could ever ‘lock down’ a kart at this track. Many people were running <3 psi in their tires, some closer to 1psi.
Here are some pictures of the track:
http://jasper.smugmug.com/2010-Photos/Thunder-Valley-Raceway/13084032_BmDQcf#!i=948268382&k=vpt9CXQ
I would look at ways to get the kart to make more grip, along with tires. There is a good chance you try everything and find out nothing works.
Don’t get me wrong, I really like that track. It’s short, you get to use all the pedals, and it’s really fun to drive. But, like you said, it can be a handful, especially in the open class. You might have to resort to the ole Scandinavian Flick.