We have been Workamping for all sorts of employers for 13 years now. While the two you first mentioned are not on our list we have worked for such places as Amazon.com, Adventureland Amusement park in IA, Disney World, Dolly World, Sees Candy, Hickory Farms, KOA's, private Campgrounds, and several other companies.
There are a lot of jobs out there, with winter (paying) jobs being the harder to come by (Our northern neighbors come down and work for free sites which screws up the market
. But we always tell employers "your get what you pay for" and we have yet to see a site we would "pay" $1200 a month for ie: approx min. wage time 20 hours times 2 times 4!
Workamper News is OK (more gimmicks than real help anymore, tho') but there are LOTS of other sources on the web. Just like hunting for a REAL job.