Probably depends on which TR3; there were at least two and maybe 3 slightly different arrangments. I haven't done one in a long time, but I remember it being a PITA both coming out and going back in.
The later style fill cap will no doubt make it easier; with the early cap I wound up cutting through the section of hose that joins the inside half of the cap to the tank. Then to reinstall the tank, I cut the new hose short enough that it would fit entirely onto the tank neck while I slid the inner piece of the cap into place. Then comes the fun part of screwing the cap halves together, without cross threading and winding up with the cap in the right orientation. Once that is done, fight the section of hose into place so it bridges the gap, and tighten the clamps. (You did remember the clamps, right?)
Don't forget to remove the outlet line and the vent line before you start with the tank.