Rubbermaid Cart for Brew Rig

I am in the process of building an electric brew rig using Cajun 10 gallon SS pot for the HLT and a 15 gallon Sanke keg for the Boil Kettle. I also have a heavy duty Rubbermaid style 24"x36" cart that I have been thinking about using as the portable rig. The cart I have has a 500 lb. load capacity which is well within my design limits even when both kettles contain liquid. http://www.harborfreight.com/24-x-36-two-shelf-industrial-polypropylene-service-cart-69444.html

I am just an occasional all grain brewer so this unit will not get used every weekend. One of the concerns I have is the ability to heat the kettles without affecting the integrity of the plastic. I plan to set the kettles on a 2"x4" pine butcher block style base setting directly on the top shelf of the cart. Has anyone fabricated a similar type of setup? Any suggestions are greatly appreciated.

I would think you would be fine as long as the wood is on there, but you could get this for half the price and have steel. http://www.harborfreight.com/24-inch-x-36-inch-steel-service-cart-5770.html