PVC sleeve from under the house to panel on porch with 2/0 SER cable. Panel was replaced and conductors were not long enough to reach terminals in new panel. Looked suspicious, so had the HO remove plywood cover over the box below the panel. This is how he extended the conductors to the new panel which is just above the top section of PVC in the photo.
Well, he did use boxes for the splices. I usually find them loose, hanging somewhere. Good catch on your part though. Are there split bolts inside the boxes? He must have worked at getting them in there and taped.
A 4" J box will surfice if you just use the rubber end of you hammer to get the wires in. The other end would only damage the wires and that would be just dumb. I almost forgot. Line the j-box with cardboard just to add a another level of protection. that oughta do it
If you have enough volume in the box for the conductors and splices but still want some extra protection, wait until the roofer is looking the other way and swipe a scrap of that self-sticking roofing underlayment membrane that they use at the edge of the roof.