Hi Shropshireman, I'm in Fife, which is on the other side of the Tay from your mate's place.
First of all, in Scotland we have traditionally had far more freedom to roam than our southern neighbours, and I believe, sadly, that it's reflected in the new Access Laws. You have a right of access anywhere in Scotland, with the exceptions of closed MOD land, railway lines, etc (not entirely sure here). But provided you use common sense and don't set up camp in someones front garden (although I did inadvertantly haul a kayak out of a river in the dark, hung my basha and had a wee fire in someones garden once. No-one should have a garden that size anyway!) you can go where you please. I do!
You also have a statutory right to camp for one night! Use it or lose it!
The use of fire is not included in the access code, but if you find a wee corner somewhere no-one will bother you unless you have a blaze going or a plume of smoke. Stealth is safe!
The trout season starts on 15th March and you can fish in tidal waters without a permit. There is a Protection Order on the Tay System which means that you MUST have a permit to fish for trout anywhere in the Tay System, including all tributaries and the River Eden in Fife. The tidal influence on the Tay extends as far as Perth and the legality of compulsory permits in tidal waters is questionable.
There have been a number of legal actions taken against people fishing for trout and grayling in the Tay but the vast majority of them have been kicked out of court. This is not the case concerning salmon, as it is against the law to fish for or take salmon anywhere, including tidal waters, without a permit.
So far as I'm aware, there is no legislation in Scotland concerning course fish.
Between Dundee and Perth, or up the A9 between Perth and Dunkeld would be good places to be dropped off for a couple of days/nights. There is plenty of natural woodland where you can disappear at will. Be aware though that this is MacBeth country, where Birnam Wood moved to Dunsinane, so look out for people dressed up as bushes and give them a wide berth... and watch the Bogles dinna get ye!
My strategy is to take a look at the map for a likely spot and head off. It's really big for a wee country.
Go for it Big Boy, and welcome to Scotland.
Cheers.