Just DIY'ed my series 1 disco at the weekend.
My advice take a wekend and DIY it.
Make sure the chasis is cleaned the day before your start - at least 24 hours in advance. Steam clean if you can if not spend a good hour or so with the preasure washer and get all the crud off.
Leave it over night to dry off then start only once the chasis is dry(the waxoyl wont adhear as well on damp/wet chasis)
I find the best way to spray is to use the waxoyl kit (comes with a preassure sprayer - bit like a styrup pump - and preasure tin and hose)
I've been told that a garden spayer can be used but dont fancy that and the hand squirt thing just looks like its more trouble than its worth
I use an old tin bucket about half full of water and stand the can of waxoyl in it and put it on the stove (yes SWMBO does hate it)and heat the water that way with the tin of waxoyl in it.
Poor it into the sprayer pump it up to get preasure and off you go.
make sure you get into all the awkward places including any drain holes in chasis.
leave this to "set" over night then apply a second coat next day if you want to go that extra mile.
I try and recoat about onece every 6-8 months but if its just a road vechcle should be ok for 12 months
If you need any advice then PM me
word of advice though
dont do it on the drive unless you put down an old tarp first as once the waxoyl gets gets splashed it dont come off