It's difficult because the salt is so absorbent.
Salt is also very heavy! If it's built up over time you probably need to rinse the salt out by running some fresh water into the ski and letting it out again. Be careful not to fill the ski too much because this will put enormous strain on the hull and can cause the stringer to detach from the hull or deck. A litre or two should be sufficient.
Run the water in, drain it out - a couple of times.
Drain as much out as you can, then leave the ski in the sun for an afternoon or two with the bung out.
You'll never dry it out completely, but that'll reduce the weight.
The only way to dry the interior is to run a pipe into the boat - all the way to the end of the hull, and then pump air in with a compressor or vacuum cleaner. I've never done it, never seen it done! But that's the theory; you have to move the moist air out of the hull over several hours.
Rob
Currently Epic V10 Elite, Epic V10 Double.
Previously: Swordfish S, Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others...