I think the pooled condensate is used to cool the coils so if you plumb a drain in bear that in mind. There needs to be a balance of keeping some and letting the excess drain. I like the idea of draining the remaining condensate after using the air conditioner and before hitting the road again. Otherwise, the pooled condensate will slop around and could end up in the van.
I have a window type A/C in my van (rear door) and had some of that water come in one time. I might have traveled downhill immediately upon leaving the campsite but I don't remember.
If you're thinking of running your A/C using an inverter then this topic:
Running small Air Conditioner on an inverter - http://www.classbforum.com/forums/showthread.php?t=2178 - will give you an idea of the numbers (cooling, power consumption, startup surge) involved. I haven't run mine on the inverter much. I've been thinking of adding a Supco hard start but I have more batteries this year & should get a chance to see how much they help first. Handling the startup surge is the challenge when running the A/C off a small inverter and small battery bank.