This would be your first port of call. Failing that,then Tvs or a similar firm could make one up,though it may mean changing the zip. Gazebos are not always acceptable on sites,but porch awnings can be used with a bit of ingenuity.
------------- Silence is golden
Duct tape is silver
It's for a Raclet Herald/Jade but may well fit a Marathon, could be worth asking (i'm not the seller, just trying to help).
I use my TT mostly without an awning unless I'm camping for more than 3 days or so. You could use a gazebo or attach a tarp to the front with a couple of poles if the weather is good
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets