The 12,000 btu A/C in our MH draws about 1KW, ~10 Amps but it doesn't have a reheat/remix mode/cycle as does most modern day automatic climate control systems. So 3.4KW is likely correct for the Prius, but given the addition cabin volume and greenhouse glass of the new HH 6.1KW might be correct for it and the RX. They could both probably be reduced to the 1KW range via running in recirculate, MAX COOL mode (bypasses the reheat/remix cycle), and then using the blower speed to manually adjust the cabin temperature to your comfort level. Purchasing and installing a coolant shutoff valve to stop the flow of HOT coolant to the heater core would also help.

You should check http://www.masterflux.com/products/sierra/
It has very useful information about sealed air conditioner compressors, the kind you find in window air conditioners, but used in boats and trucks, rv's and things like that.
I found a 12V air conditioning system in a wrecked boat, they sold me the complete system for only 80 dlls, but had to pull it out by myself, there I found out the manufacturer of the compressor, so I got all the information from these website.
The compressor itself is so small, I could stash it in a metal basket under my Blazer, away from the front compartement, former engine bay, because now is all full of batteries, cables, inverters and such stuff, as soon as I figures out about the refrigerant circuit and the needed components, to use the same evaporator and blower in the OEM dash, I took the blazer to a friend who is a certified A/C techie, so, he mad all the needed hoses, tubes and electric controls from the dash, since I live in the desert, where the average heat is over 120 F in summer, A/C is a must to have, now, I have the advantage to leave the A/C running even with the Truck parked, on the 4 batteries designated for the A/C it works for straight 4 hours between charges, cooling down my cabin around 75 F parked in the sun, that's very comfy doesn't it?
I used OEM condenser, evaporator, dryer, cluster, blower, etc. all the Techie did is redirect the hoses from where they were when the truck had an engine, and pulled them under the truck, where I stashed the comressor, very simple and effective.
Before this last conversion, I made a metal plate to mount the OEM compressor and an electric motor to drive it wih a pulley and belt, with a 1.5 HP, permanent magnet 12V motor is enough, but, It will DRAIN your batteries in about 1 hour of use, it works fine for short trips, but why limit yourself?

"..wrecked boat.." "..The compressor itself is so small.."

Maybe TOO small.

A marine A/C is typically designed to extract/transfer COLD from water, much more efficient than an A/C that extracts COLD from the atmosphere.

Unless you install one hell of a large condensor your "small" compressor might not have enough capability.

You may be "barking up the wrong tree".

The inverter driving the A/C compressor in these hybrid systems may be, should be, especially "tuned" for the application. While there is little reason to improve the operating efficiency of household A/C systems there is EVERY reason to do so here.

I would fully expect that the motor itself, much like MG1 and MG2, is of a permanent magnet rotor brushless DC type. In all probability the A/C compressor inverter used in these HSD systems makes use of PWM, "dutycycle", modulation of the variable frequency output square waves.

Many high power, >50HP, A/C motor used in industry today even make use of a technique to recover energy from the motor's back EMF. Sweo/Baldor motor drives, for instance.

Given the need, desire, to reduce hybrid battery energy consumption the inverter driver for the A/C compressor may be a bit of an unusual design. As, undoubtedly, are ALL the A/C motor/generators and "drives" in these HSD systems.

The electric A/C in my Solectria Force maintains a temperature drop of about 20-30 degrees F. It uses slightly less than 10 amps at a nominal 156VDC. The design is a permanenet magnet motor driving a compressor. It becomes very marginal as the temp gets above the high 90's.

I would be very confident that the design of the masterflux unit would be much more efficient.

Your lucky in that a small truck has a small cab to cool and not so much in the way of greenhouse glass.

10 amps at 156 volts would normally equate to ~4500 BTUs of electric heating capability, or, also typically, 13,000 BTUs of cooling using a comrpessor/refrigernat system. That's 1 ton+ of A/C cooling capacity.

"..marginal above 95-99F.."

Should NOT be...POOR design.

Well, this particular compressor is equivalent to a 6,000 BTUH room air conditioner, but runs off 12 VDC, and has the great feature that you can put it horizontally or vertically, since is a scroll compressor system, doesn't matter how you put it or how much you shake it, the condenser in the front grille has two 14" high performance fans, one comes on when the compressor does it, the other turns on with a pressure switch, for protection, so, if the outside air is warm, under 100 F, only one comes on, but, if is very hot, over 110 F, the pressure rises and the second fan comes to do its job dropping the pressure immediately, as I told you, in a hot day over 120 F, my blazer is at 75 F inside, even parked, so, if I'm going to the 7 eleven or to the bank, I just leave the Air Conditioning running, so, when I got back, It's nice and cool, not all hot and blistering seats, ok?