Ya I always cut the hole as big as possible then on the last install I did I found a rubber hose that just slipped over and then wrapped it all with heat tape the thin silver stuff to hold it all in place. Worked really well...
Bit tricky to see but it was rubbing in 2 spots. 1 where it comes through the tunnel and the other where it passes by the plate underneath the header bellows.
Pulled the tube today it did not wear through but I plan to fill it in, remove the rubs spots and reinforce it so I never have to worry about it again.