Cross Border Navigation

Hi all
This weekend I am going from England to France then onto Belgium.
My problem is; Firstly, do I have to switch maps at each border? and secondly, how do I navigate from eg St Omer in France to Brussels in Belgium if I don't know the shortest route or where the border crossing is?
Sorry if this is a basic question but I don't use the European Maps that often and its usually just staying in the one country.
Thanks in anticipation
Garry
P.S. Any other tips would be gratefully accepted.

[getsurfers]

If you have the GB plus maps instll/uses them, use that as it has all the main roads for europe (assuming you have the western europe edition of TT5). Then simply switch countries once in that country for local/smaller roads.

Thanks Getsurfers,
I do have the Plus maps for GB, France and Benelux and TT5, if I understand correctly I can plan a route from St Omer to Brussels and this will take me there via the motorways/major roads.
Cheers