shouldnt have no prblem using rubber lines . my 94 ford explorer 4x4 had rubber lines stock like your trying to do but dri rotted . so i swap them out and put new ones in . but yes they are pressurized a little but not that much just make the hose as short as you can and no kinks in it .. jsut roll the ends of tranny lines metal /alumin rods so that it has a lip on it for the rbubber hose to hold onto . i took a small screw driver and rolled it around 360 inside the the metal line to make a lip . just incase any pressure built up it would have something to hold onto (SOUNDS LIKE YOU DONT HAVE A LIP ON YOUR LINES ). never had any prblems since . i ran this truck this way over 6 yr before i solld it .

i also had a buddy that did the same thing above and but put a alumin fuel line inside the rubber hose for a more solid application not sure if it makes a diff but he felt more secure that way .

just make sure you put a LIP on the end of the tranny lines (BOTH SIDES )and you should be fine . I WOULD USE A BRAIDED RUBBER HOSE OR A THCKER HOSE THAT IS HARDER TO BEND CASUE TRANNY FLUID DOES HEAT UP SO SOMETHING WITH A HEAT RESISTANCE.

tranny lines are just pressurelized enough to move the fluids from point a to point b . nothing extreme