Trouble with shipping weights / multiple boxes

I need UPS shipping to quote shipping based on multiple boxes. I have a clone of freeoptions module running that sets anything over 150 lbs to flat rate shipping of $200. I have that setup to quote shipping on some very heavy items I ship on a pallet with freight shippers. The problem is, whenever someone orders a large quantity of smaller items and their combined weight goes over 150lbs it switches these to flat rate $200.

I have the max box size set to 500 on the configuration>shipping/packaging. When I drop it to 50lbs it solves the problem for smaller items but then allows customers to ship a 300lb product in 6 boxes which is of course impossible. Does anyone have any suggestions? Maybe freeoptions clone isn't the best solution to ship these heavy items...

Thanks,
Phaylon

Google for
zencart advanced shipper

I've already looked into that module and from the demo, it isn't very clear on if it would help me. I would prefer to find a solution in the available code before spending $$. Thanks for the suggestion though :)