Fitting door seals is a acquired art you can only learn from doing it.
Sometimes a little lubricant might help but you should use the proper formulated "rubber grease" stuff. Washing up liquid can seriously shorten the life of a seal.
Sometimes the right sized socket on a very long or maybe a couple of extensions might be necessary to get past a front fitted concrete or metal counterbalance weight in order to loosen the boot's retaining clamp. You usually access this from the top by removing the lid. Of couse you get the odd machine where some fool, in initial assembly, has arranged for the clamp to be in such a position that the drum has to be removed to make it accessable.
Skinned knuckles, tired fingers and aching knees are par for the course
but once used to, it's regarded (in most cases) as a bread and butter job.