what you need is the ez3 usx, even the ez3 tadpole may not be as strong. But it will be a close runer up.
unfortunatly it will caost time and money to up grade their trikes, still thats under $2000 hopefully.

I am over three hundred, can't burn it off....bikes are too efficient. The best trike to get is one of the light foot machines but they start at $3000, the only good thing about Sun's machines are the heavy duty frames. the wheeels are usless, you need new custom wheels with BFR rims and good hubs and thik stainless steel spokes.

good high pressure tires are essential for large weights, and I dont mean the whimpy one inch racing tires. 2" tires are the best....with 20" diameter you neeed 110psi and on a 26" wheel you can get by with a 70psi tire. shlabe merithon plus 1.75" 70psi 20" may be ok and the maxis hookworm 1.95" 110 psi amy be ok but I dont like the way tread pix up glass.