Sadly, I will be away at work (again/still!), and have not managed a Mylor meet so far...but as a local (Fowey), this may be of some help?
I'm sure Mylor Marina will accommodate you; we've left various boats/cars there over the years, but they will (of course - this is Cornwall after all!) charge. Phone and "book" if I was you.
The key to an easy drive to Mylor is to start by turning off at Exeter (at the end of the M5/start of the A38 to Plymouth) onto the A30 for Okehampton & Bodmin.
DO NOT go A38 via Plymouth (which many still think is the main road, as it was for many years).
Incidentally, heading down/West is free, but if you come back (heading up/East) via Plymouth, you will be hit with a hefty toll if towing.
We now have dual carriageway (and electricity even - though often no mobile phone signal!) right across the moor(s); the new roads were finished last year, past Bodmin, and now as far as the Truro turn off A39 (Trispen - Carland Cross, by the Toyota dealer). This is where you would peel off left for Truro & onwards to Falmouth/Mylor.
The A39 here is newish too, and easy motoring.
This only leaves 10/12 miles on old-style Cornish roads.
After going through Truro (v small city/county town) its only the last 5/6 miles that can be a little nerve wracking, on "traditional" narrow/steep/wet lanes!
When towing:
The first "brown sign" to Mylor YH at Perranarworthal (left, just past the Norway Inn (very prominent) is (imo) not the easiest route with a boat on the back. The hill is very narrow/steep/windy, and I've had past-problems (when I did not have a 4x4); don't stop going up a wet/leafy hill!
This being the main sign-posted route to Mylor YH, it's not uncommon to meet another boat coming the other way, just to make things even more exciting!
The next left turning (about 1/4 mile on?) is easier; less steep/windy but still narrow (pretty-much single track I recall?); it's not posted for Mylor YH.
Personally, I prefer to continue on the A39 towards Falmouth, via Penryn, on the old B 3292, then double-back towards Mylor YH.
Incidentally there is an excellent, and more reasonably priced chandlers (usually - but Mylor are getting better. If there is such a thing as a reasonable chandlers - it's relative! ) just past this turn - MacSalvors.
Hotels - depends on your style/budget, but there is are newish Premier Inns at Bodmin, 40 miles before Mylor, (next to Asda garage), and Fraddon too (a little closer to Mylor) - both just off the A30; parking/access there is easy.
There is another, much further "up"/East, at Exeter services (end of M5 - about 100 miles/2.5 hrs from Mylor?) which is also very easy/convenient.
There are of course many much nicer hotels about, but if I were towing these would suit me.
Beware, if you leave the main A30 roads can quite quickly become difficult for towing if you stray too far. I use the Google "fly-through" to pre-check, when possible.
Hope this helps?
PS - Don't forget your "Kernow" courtesy flag; St Piran's Cross
...and remember that when we say "hedge" we mean earth/stone bank full of pointy rocks, often granite - so don't get too close when towing!
ADDED 12 MAY - On the subject of Food/stops en-route:
Forget Exeter Motorway services, use Lifton Farm Shop, Lifton, Devon, PL16 0DE
Open appx 0800 > 1700. Very popular with passing "locals", highly recommended
Easier access, plenty of parking, better food & better value than Motorway services at Exeter.
http://www.liftonfarmshop.co.uk/contact-us/location-map(just East/up from Launceston - 40 mins West of Exeter/appx 1.30 hr away from Mylor
