My suitcase will be FULL. Am considering what I use for my fishing rods on top of vehicle. A 6” pvc pipe with end cap glued on one end and a lockable cap on other, then cut 6” pvc to desired length. Have looked all over for something on internet- Either too long or to flimsy ( document tube). Would take fluid head off and put in suitcase and put tripod on cloth sleeve it came in and possibly some additional padding, if possible. Do you think this would be acceptable?The 3563 XLS is 28 inches fully retracted. I would pack it without the head in a suitcase. Most likely you will need to pack it diagonally. It it is still too long, your options are to remove the tripod feet to save a little, or possibly the bottom leg sections. You'll need to be careful with the bottom leg sections to be sure you assemble it properly and don't lose or break the sleeves. You might use a rubber band or plastic wrap to secure the sleeves safely. I would pack clothing between the tripod legs to reduce the possibility of excess stress on the joints or hub.
I always travel with my ballhead in a carry on. That may not be practical for a gimbal head, but I would do the same with that if possible. It's a lot easier to borrow or replace a tripod when traveling than a ballhead or gimbal head with custom plates.