Hi Rod, R&D, trial and error, controlled experiment, it is great result when with the aid of a bit of nouse that you were able to achieve the desired result in the first round. Good going
And thank you for suppling all that info.
Montynut, if you cannot find an original in time and don't want to make a mold? you better get a blank foam of Les quickly and get to work.
Mark out your foam with a permanent texta.
If you intend to use an original seat cover? you will need to do a smick, accurate job of preparing the blank foam. Obviously you will need an original seat to copy the three dimensional profiling from.
A little bit of prep will make it a lot easier in the long run if you intend to produce a perfect original. Use an original seat as a model to raise profiling templates from. Cut from cardboard a template for the beginning and end of each of the three dimensions runs first. If the cut run changes angle(deviates in direction) along the way, best to make an intermediate template for the cross-sectional profile at that point. Then make all of your templates
at least 3mm bigger, three mm is fine if you have smooth cutting skills. This is to allow for a small amount of surfboard style shaping at the end and also the finished foam needs to be a couple of mill bigger over-all to produce a taut fit for the cover. Use the templates to assist in marking out and again as finishing guides when sanding.
All though Makita sell a cutting tool for foam, it is expensive. Use a large band saw
very carefully. Very slow controlled hand feed. An electric carving knife with long blades. Be very aware of where the other end of the blades are cutting, or its back to Les for another blank. I find it impossible to witness both entry and exit points of the blades at the same time. Unless you are sure, stop regularly and check that your cut is proceeding as planned.
Have a bucket of water next to you with some dish washing liquid added. Dip the cutting blades in it, each time you stop to check your cut. I assume you have a supply with earth leakage and fill the bucket no further than the depth of the blades of course.
For final shaping, mount your seat base to a solid non moving carpenters style workhorse or beam. Then glue the new foam to your seat base with that yellowish contact cement. Use a hand held 3" belt sander to
slowly and gently finish.
Most seats have a radius along the top longitudinal edges. To produce this small radius, grab your belt sander and use to it in the same motion(rock filing) that a Fitter Machinist would to hand produce a radius and other materials, be it metal, wood, plastic etc.
The best way to cut the foam is to knock up a hot wire cutter. Grab an old fan heater of the council clean up. Unwind the heat fulfillment wire. To straighten the wire, re-kill it. You can do this by straining it and pulling it back and forth over the curved edge of a piece of pipe.
Then strain it like a bow string between two mounting points. Get a car battery as source. To control the cutting heat of the wire, use the demister fan control switch and resistor out of an old car wreck. Mount a tilting plywood guide table and the cutting hot wire obviously replaces the bandsaw blade.
Easiest to get a trimmer for a custom made cover if in the end the new foam has turned out a bit ordinary, Good luck.
PS; personally I reckon Rods method is the go 
