I use Anquet which I find very convenient. You can hand draw the route with the mouse which is very easy. I havenot bene albe to do htis with other systems
I have not been able to send .gps files direct from Anquet to Satmap or vice versa.
You have to send them to a folder and then you can get them from there to Anquet or with SatSync.
I haven't seen anything which makes this clear but it works wonderfully once you know about the need for a folder as an intermediary

I'm not familiar with SatMap, but use the OS maps app and this uses .gpx files. You can upload routes that you have created onto the online site: https://osmaps.ordnancesurvey.co.uk/
There are conversion sites to change .tcx files into .gps files such as this:
http://www.gpsies.com/convert.do;?language=en
Which I have used and works well.

No experience of SatMap, except a report that it has a problem with start and end points that are identical.

Two suggestions that may be worth a try:

1. http://www.osola.org.uk/rides/gpsuploader.htm from Bob Osola.
The section 'View UK GPX & KML files on OS Maps' is probably most useful.

2. http://www.plotaroute.com/ Good design and quick to implement practical suggestions and fixes.
Plot, share and download routes. Upload existing GPX files. Measure sections. Use handy route profile tool.

Both the above measure the E22 route Dover to Kirk Yetholm at 680 miles so no problem loading long routes.
A good recipe may be to develop the route using plotaroute.com, download the resulting GPX file and display it in Bob Osola's utility.

Let us know how you get on.

I am presently using SatMap's xpedition service online at www.satmap-xpedition.com for route planning but I am having difficulty getting my .gpx files (which are complex - I'm planning at the equivalent of 1:25000 to get an accurate mileage count on a 500+ mile route) to load sometimes waiting in excess of 20 minutes and sometimes it just doesn't happen at all. I have been invited to send the gpx file to SatMap "for examination" but before I do this I am wondering what alternative online route planning services I might consider?