I want to replace my rear struts, but not sure if I need to same length or some with a shorter extended length. My car has Suspension Techniques springs and Tokico struts. The springs are not compressed by the cap, isolator, pocket on the strut and tight against the spring pockets when out of the car. Is the weight of the car enough to keep them tight against the pockets or do I need to look for a different strut?

Are you saying you didn't have to compress the spring to assemble the strut?

Yes. I can remove the top nut w/o having to compress the spring. The spring will rotate around a little, but it ultimately contained due to the shape of the spring pockets.

It should be normal with those springs, try to do a search for ST springs, you could use some for the front and put a spacer under it to fill out the difference in length.