X2 the more on top. 

Actually, I'd just get a new bed and save myself the environmental and chemical damage.

EDIT:
After looking online and finding tons of "it's impossible" postings, the consensus is that you need to find a place that has a sandblasting setup that's sized to do the entire truck bed/cab/etc.  It's usually a giant tower and they run it in this enclosed space for 30 minutes or so.   Everything comes off.

Any other option just won't work or will literally take like 50-100+ hours.