Installed a heap of these, usually limited on where we can put it by aircons, roof vents, solar etc so i usually just lay the antenna on the roof and work it out from there. one thing to watch is the access to the winder handle, you don't want it above a cupboard or in a hard to reach place, we have even mounted them on a slight angle to clear roof objects.
to run the coax, you have to realize that the roof has cross braces, so you can only run the cable sideways without risking trying to go thru a brace. once the hole is drilled and a hole thru top skin only for the coax i open up the cavity inside a bit so i have room for the coax to have a joiner inside the roof near the shaft hole.I use a long spring out of a camper lifter arm, heat up the end with a blow torch and melt my way thru the foam working from inside the van, you can even steer it to some degree. and i drill a hole in the ceiling near the edge and aim for that. then it's a small bit of wire and some string to fish a line thru the hole, once thats done you can pull the coax thru, HINT, don't tape the coax to the end of the string, leave enough loose so if the tape break the string is still in the hole to try again, i usually feed up toward the antenna instead of trying to get the coax out a small exit hole near the roof edge.........
A grommet on the exit hole neatens the thing off. then run the cable down one of the pockets in the tent for the folding spring (which is another thing to consider on where the hole in the roof will be) and out into a cupboard again with another grommet. the booster you can put anywhere that you can run the coax to at the back, but they are pretty ugly at the back so i aim for the side of the split system or microwave to hide the back of them or use a jayco cover to hid them a bit, remember you need to get 12v to this as well. the factory just use a hole saw, which is a pain to get the booster in with the coax connected, the new boosters are easier, but you still need to add a coax point near them as well as they don't have one built in.
Once it's in and booster is on you should be getting <12v at the antenna end of the coax, another tip is don't shorten the coax, it's hard to find a proper crimp terminal for that size (or if you do find one tell me!) just fixed a customer job where he used just normal pliers to crimp the terminal and shorted out the coax ...........
make sure you use a continuous bead of salastic under the winegaurd base and another circle around the cable entry point as it's a trouble spot if not sealed correctly, after it's screwed down put another decent bead around the outside and cover the screws as well, seal the cable entry point with a heap as well and push the coax cover onto the wet slas to get a real good seal. water can run down the coax and find it's way in so use heaps (pity the next bloke who has to get it off!) i usually finish it off with soapy water to get it lookin cute
a handy hint ..... if you have a pair of conduit cutters (electricians use em all the time) they are great for shortening the handle tube to the correct length, make sure you don't go too short as you need to be able to pull the outer ring down to rotate the antenna. cutting the alloy shaft too short prevents this from happening.
It's not a job i take lightly as one mistake can ruin a roof from a botched job or water ingress at a later time, so make sure your feeling comfortable about jumping into this one.