Remote controlled railcar and coach

My son bought me an I.P.Engineering 4 wheel coach kit for my birthday last year. I made this up as per the instructions and fitted interior lighting. I decided to paint it Oxford blue and cream, and lettered it G.W.R. after my son (yes - those are his initials!).
Over the winter whilst the coach was sitting on the shelf, I speculated that another kit could easily be converted to a small railcar. I duly purchased another coach and set about converting the body. I cut two window holes and a space for the engine cover in one end. I also cut a strip from the bottom as this end would be sitting on the floor instead of beside it.
The sides were reduced in length by one window. The thin plywood was easily cut with a sharp knife.
I glued the body with PVA glue and let this dry held with rubber bands.
My original plan was just to fit a simple on/off switch. However I came across a very inexpensive (under 5 UK pounds) racing car with 40MHz remote control in a local shop which got me thinking. The range of the remote was surprisingly good at around 20 feet, and it provided forwards and backwards control of the motor.
The car contained a very useful motor as well as the simple remote board. This was duly removed, and my son gained the now free-wheeling car to play with (he is only two!).
I fitted the remote board, 2 x AA battery holder and on/off switch inside the engine compartment which was fabricated from offcuts of 1.5mm plywood.
Since I wanted the option of allowing the railcar to potter around the garden unattended, I fitted another switch underneath the body. This switched the power to the motor either via the remote board, or directly from the batteries. I fitted a 40:1 gear onto the rear axle. This was driven via a worm gear fitted to the original car motor which was araldited on a wooden spacer under the floor.
In order to be able to get at the batteries and electronics, the top and front of the engine cover slide on and off as a single piece. I used some small gauge wire mesh to simluate the radiator grill.
I wanted the roof to be removable as to allow easy access. I thoroughly soaked the plywood roof and then fixed this to a paint can of a slightly smaller radius than desired for a week using duck tape. This is a very easy way to bend thin plywood, and it holds its curve indefinately once released. I cut three curved 4mm plywood formers which I stuck under the roof, and connected these with 1.5mm strips. This allowed the roof to be dropped on to the body and held securely in place.
The structurally finished railcar perfomed admirably on its trials. I fitted a windscreen wiper from a 1:18 scale car which I had in my scrapbox. In due course I will add white LED headlights (if you know of suitable round railcar like lamp holders I could fit these in please let me know), interior lighting and a driver.
I found that on my line with its 1:80 gradients, the railcar would go round happily on its own powered by two 1.2V NiMH rechargable batteries. However it needs the little extra voltage of two 1.5V alkaline dry batteries if pulling its trailer (my original coach) using the remote control. So far it has run for at least 5 hours on a pair of these.