Protect? As in, from the elements? From memory, most on here will say do nothing. There's not much a journey by road will throw at it that a journey at sea will not throw worse or a wash down afterwards will not sort out.
I cover mine but only so I can use it as a glorified trailer for all the holiday paraphenalia
Check your insurance too for trailering on the continent. I'd be wary of a cover in case it gets blown off. Also, don't forget to strap the boat down onto the trailer...something that doesn't get done locally very often.
I think mudguards are a legal requirement, though I suppose if your tubes overhang enough then perhaps they would do an adequate job . I tilt my engine up for short journeys but would perhaps leave it down for long journeys so that it is braced against the transom. I'm sure there will be many differing views on this
Without mudgaurds you run the very real risk of spraying stones/ glass etc all over the underside of your boat / tubes which over 700k will I am sure do you no favours .......giving you potential punctures in the tubes and chips in the hull.
Mudguards - prop cover - secure load - all legal requirement. (as are lights!).
With regard to securing not many here are a fan of the "strap over the toobs" approach. Mostly down to wear of the toobs, but all you need is the sun to go in and your nice tight fixings will go very slack..... Use the transom eyes and the bow eye - use an extra rope (or painter) to lash it vertically down to the drawbar at the bow eye.
Regarding covers my internal jury is still out on - Having towed sailing dingies with covers, they are a pain in the rear to keep on, and unless are drum tight (and even then they move) will flap & chaffe. not such a big issue on a fibreglass hull (the cover looses that battle!) but on toobs..... I am toying with a jockey cover just to keep he seats & instruments clean, but reckon the rest of the baot can stay open.
I tow at about 1/2 tilt unless it sits very high on the trailer down runs the risk of catching the skeg ona speed bump!
Also a good idea to leave your elephant trunks / drain bung open - if it starts raining you would be amazed just how much heavier your trailer will get.....
but only so I can use it as a glorified trailer for all the holiday paraphenalia 
. I tilt my engine up for short journeys but would perhaps leave it down for long journeys so that it is braced against the transom. I'm sure there will be many differing views on this 
