Westie,
The transport fee never includes launching.
My friend, I fear you have more of a challenge here than you are counting on with a 255 (which is a great boat, if not the greatest boat in the world).
My rig is a GMC Sierra 2500HD diesel with 20,000# parking pawl and an Allison Commercial transmission rated for 12,000# deadweight towing/15K with wt distr hitch. On launching 2 weeks ago, with the truck in Park and the boat engines in neutral, just the rig weight alone skidded us down an extra 2-3 scary feet down the best ramp on the Gulf Coast (a WW2 seaplane ramp that extends to 9 ft underwater at low tide). We use HUGE solid rubber chocks to prevent this, but had not deployed them yet because we never had this happen before even getting the trailer front fenders 2 inches under water.
My best method for launching requires the somewhat scary 'slam on the brakes at just the right moment to jerk her off' technique, which has my rear truck wheels in the water almost up to the brake rotors before this can happen, and I have a Long Bed pickup and a 12" extended tow bar. If you forget to disconnect the transom straps or the safety chain or the bow strap, and/or forget to place your HUGE manly chocks, your tow truck WILL go underwater. Your Lexus is WAY to nice to even risk it.
With my new 4 blade props in Reverse, I have managed to skid down the whole truck/trailer/boat rig down the ramp in Park when the trailer isn't in deep enough.
Have your driver watch for the anchor to start to 'dip down' to indicate when the rear of the boat is starting to float. Even then, there is a lot of friction/wgt on the front of the trailer and you will not reach the 'magic spot' (at least with my rig) without the added inertia of the 'jerk off'. A friendly Sea Tow captain used to big trailer able cats taught us this at our first launch.
The guys and ladies who transport boats for a living are likely to be both knowledgeable and reasonable folks, and I suggest you ask your transporter if they would consider launching with your help if you provide the chocks for a +/- $200 under the table cash tip if your ramp is real close. Keep in mind she has another pickup maybe today. $500 would be well worth keeping your Lexus out of trouble and almost guarantee cheerful help from her or a buddy with a 2500HD truck and some big boat experience.
Other 255 owners launch and load routinely by themselves, but we find it much easier as a 2-partner exercise using Ear-Tec 2-way comm headgear rather than hand signals.
You are right that the problem is not your engine, or long term towing, but that of of a 2 ton SUV (less?) trying to slide a 5.5 ton tow pkg down a slippery ramp into water without the tow pkg being in control of the puny SUV. This boat don't float off the trailer in shallow water, though it floats in only 15 inches of water just fine...do you follow me here?
I hate being an outlier among all these experts, but I say DON'T EVEN TRY IT. PAY WHATEVER IT COSTS AND STAY SAFE AND HAPPY.
PM me for anything I can help with or phone #, I just cringe at the thought of a new owner of a great boat making easily preventable errors without advice...
Cheers! and Best of Luck!
And what is $200-$500 compared to what you have already invested?
John