I was hoping someone could share with me some tips....i have 2 chocolate buttercream drip cakes that I need to transport for a 2 hour car journey on good friday. 

I plan on finishing them thursday morning so they will have plenty of time in the fridge so set, i will also put a dowel through the centre for a little more stability....i have a crate in which i will put both cake boxes in but some more tips would be greatly appreciated!!

Just nervous as we are due lovely sunshine and i dont want them to melt, slide and be a mess when i arrive. 

Let me tell you I have done that many, many times:)   You don’t say what size they are —like 6” or 12”ers    There’s no need for a center dowel unless it is stacked tiers, & even then I’ve delivered many w/o it   It sounds like you are very over-worried:)   Make sure the cakes are sitting level & there is nothing else around them that  might fall on/against them   Make no sudden turns or stops & just in general use good driving habits   I’ sure everything is going to be just fine   I have never had b’ cream melt & 95%  of my work was ABC  

yes and you also want to keep the cake and box out of sunlight even if it is boxed -- I sealed my cold cakes into corrugated cardboard boxes because they hold the cold for several hours -- the cake should not be allowed to slide in the box -- so the box either needs to be the same size as the bottom board or put a piece of nubbly shelf liner underneath and you can put one under the box as well even if it is in a crate because you don't want it slipping around at all -- nothing wrong with a dowel in the middle if you need one but if the cakes are cold and kept cold you don't need it --

Ditto all of the above.  For the last couple of years, I've been using Sedar Yenner's Instant Portable Fridge.  It is fabulous and free.