My pressure washer has a foam tip and it does a decent job of foaming the soap onto a vehicle. I then can hit it with a 15 degree tip and get the dirt off. If I was off-roading in a jeep, that's exactly how I'd do it. I only use a pressure washer soap that the pump can handle.
Here's how I actually clean RV's and vehicles: Mix some car wash soap in a bucket. Use a soft bristle brush on RV's or a soft cloth mitt/brush on the cars and trucks. If I'm cleaning your Bentley it will be the mitt. I use the garden hose to rinse but I have a MR Clean sprayer that has a cartridge to soften the water for last rinse and leaves no water spots. If I'm getting intense, I use a California squeegee and a chamois to wipe down the rinse.
A few years back I scored a gallon of Parfe liquid spray wax at the reuse/recycle center. It is great for aluminum RV siding, snow blowers, and the lawn implements. Made my snow blower chute clean ice and snow like nothing before.
On my good vehicles I use Meguiar's products mostly and I have an array of rubbing compounds, waxes, and polishes. I also have buffers.
I went with black vehicles for a few years (still have three) and they are a chore to keep the shine on. I am working my way out of black as a body color.