These images and ideas are literally "thrown together" as it's easier to put a few images on a web page and refer interested folk to that site rather than keep e-mailing them out.
I have been operating portable, in one way or another, since 1977. Portable operation has usually involved either transport by, or operation from, a vehicle. This page covers my most recent operating on 6m, but the general principles apply to other bands.
The image above shows my 25 foot telescopic mast which is slotted into a "drive over" base plate and supported by 3 guy ropes. The mast is the top section salvaged from an old pump up mast, the guy plate is triangular and made from a scrap sheet of 16g aluminium plate (below right). Note the spacer below the guy plate to avoid snagging the guy lines on the clamp... It is an offcut of 40mm waste water pipe. The drive over plate is a home made (by someone else) heavy duty unit that is far better than those often advertised on ebay.
For anyone wanting to make a copy of the drive over plate, the dimensions are as follows:
Base plate 14" x 19" x 3/16" steel. Edges are 1 1/2" x 1 1/2" x 1/8" angle, the rectangular tube is 18" x 2 3/4" x 2 3/4" x 1/8" and is welded 2" from the edge of the base plate. There is a lip on the edge opposite the tube which has been folded up from the base, equally a stiffening strip could be welded on there instead.
The advantage of using a square tube is that it allows the mast to be locked in position by means of a wooden wedge or two: