Since we are dreaming, my ultimate Trawler would look similar to Tad Robert's Passagemaker Lite 56
Passagemaker Lite 56 - Tad Roberts' fast, seaworthy, fuel-efficient long-range passagemaker, however it would have a 12' beam, instead of 13', to make it transportable without a pilot car in California (CA). It would also be a little longer than 56' so I could fit in a second state room with a island queen.
I'd keep the forward stateroom(s) but I'd lengthen the Pilothouse to make a combined Pilothouse and saloon with the galley up and nearly 360 degree visibility. I'd move the engines under the enlarged pilothouse and have a full beam master stateroom aft of the pilothouse. The upper control station would be above the aft stateroom and aft of the pilothouse to keep the center of mass low for stability and the height low for transport-ability. Some of the increased length would be used to provide a decent sized cockpit for fishing and diving. I estimate the total length would be about 66', which would make her very fuel efficient with a L/B of 5.5.
As long as the beam is <=12', the height on the trailer is <=14' and the total length with truck is <100', it could be transported without a pilot car in CA, OR and WA (along with most Western states i.e. AZ, NM, TX ...).
If the boat was going to be too unstable with a 12' beam or to improve the layout, the beam could be increased to <=14' with a proportional decrease in length to ~56'. This would necessitate a pilot car in CA (but not OR or WA) and increase annual round trip to WA cost by ~$2,000, however the reduced length would save ~$1,500 annually in slip fees (in So Cal). L/B would be 4:1 so it would still be pretty fuel efficient. Another advantage of the shorter length is it would increase the number of marinas that could accommodate her.