im on a tight budget so im going to make a homemade single stack, it looks like i can just do a 90 straight up where it goes under the bed. i need to know what they make to hold the tubeing from moving around where i pokes out the bed or if im on my own fabing something up. then ill top it off with a used semi stack frome the local semi graveyard. thanks for your help.

 

I made mine for free. jsut a4 inch piece of flex and a 90 up into the bed. then a 4-5 reducer to a piece of bulk 5" pipe i cut at an angle. I used a stack clamp i robbed froma peterbilt in the yard. bad pic but here ya go

 

You should be able to get a piece of Unistrut and a pipe clamp at Grainger or a plumbing supply. The clamps come in any size you want. This is the same thing I have seen on most simi stacks and very strong. I would use one low and one high and you could pull with it.
And like he said above, use flex as the bed moves a lot.