Things to consider when packing the body off the chassis.

1. NEVER add more or less packers than suggested in the parts book at the front and the back of the chassis. This is easy to see once you think about it. At the front and the back, bumpers have to fit and with limited wiggle room, the packers need to be as stated in the parts book to ensure bumper irons will fit. This applies to the floors too although if extra packers have been needed at the A and B posts, the odd extra packer might be needed under the floors to prevent too much straining when the floors are bolted down.
2. ONLY adjust the door gaps by adding or subtracting packers from the recommended number at the A post and B post.  
3. Rather than use large numbers of rubber packers at the A post, use steel shim 619395 ( us this at he B post of TR2-4 too) and 619396 at the B post (TR4A-6 only). place these in between rubber packers.
4. Ensure the body and chassis are loaded with ballast to simulate engine, gearbox, axle and a fully loaded body before completing the task otherwise you will have a lovely set of door gaps when the car is empty, and may well not be able to open the doors once the shell is loaded up. Ideally have the suspension fitted, even if only slaved on so the car can rest on its wheels. 
5. if after all this advice you cannot get the body to sit on the chassis unless there are zero packers at the A and B posts and you need large numbers of packers at the front or rear, your chassis is bent and you need to either mend it or replace it. As RevingtonTR make new chassis we can help you here with a new unit or a repair if possible.