Originally Posted by Polwart
I am guessing nav lights use 5/10W bulbs. So say 2x 5W for side lights and 1x10W for all round white. Thats 20W with them on. 20W at 12V = 1.7 Amps. So you would expect to get around 5 or 6 hours from a battery pack - but then have no power left for lighting the trailer/slipway.
Personally though I would investigate fully if there is any lighting coil on the engine as that would be much better.
Many thanks for the sound advice - was looking at nav lights & all-round white today as well as clamps to secure to my A (single) frame. Next step would be to wire them up and lead them to the powerpack under the console.
But as a longer term solution, will take your advice and have a detailed look at the engine for a lighting coil.