Rodiganwhat kind of wax are you using? Dome specific wax should hold up longer than 1 session....
powderwhorWhat you need is very hard wax. This type of wax is meant for really cold snow but it works great in harsh conditions because its so hard that it holds up to abrasive forces longer than anything else. It's actually what we used when I was racing in the summers at mount hood because its the best way to protect your skis from all the salt, despite the fact that it was usually 50+ degrees F outside.
Swix CH6 is probably your best bet because its meant for very cold snow and its relatively cheap, especially when you buy a brick or two of it. Make sure if you decide to use cold weather wax that you spend considerably longer melting/ironing it in (rub on will not work at all) compared to regular wax. The wax is so hard that it essentially cools the second you take the iron off of it, so you need to do a lot of nice slow passes to get the wax hot enough to actually activate the bond between the wax and the base. Your top sheets should be warm to the touch along the entire length of ski if you have ironed long enough. Also, make sure you drip on enough wax or you will burn the bases, particularly because you have to run the iron over the ski for so much time.
Hope this helps!