Trouble with the Portuguese.

I am having problems with The Portuguese variation of the Scandinavian Defence.

After the book moves: 1.e4 d5 2.exd5 Nf6 3.d4 Bg4 4.f3 Bf5 most of my opponents are playing 5.g4!? to which I reply 5...Bg6

This move (5.g4!?) is not mentioned in 'Starting out: the Scandinavian' by: Jovanka Houska or 'The Scandinavian' by: John Emms.

Selby Anderson says, 'after 5...Bg6 6.c4 e6! Black can play for rapid castling and counterplay on the f-file.', but this never seems to work out well for me and I'm always finding the games a bit of a struggle.

As a result I am seriously considering playing the non-book move: 4...Bd7 or deviating earlier with 3...Nxd5

Or converting to a completely different variation such as: 2...Qxd5 3.Nc3 Qe6

Any suggestions please?

This is what I have seen in the critical variation of the Portuguese.

The problem with the Marshall Gambit (1.e4 d5 2.exd5 Nf6) in the Scandinavian Defense in general is that black needs one more move to make it work.  Black is pretty much waiting for white to error first to equalize.  Is it playable?  Sure.  But is it equal?  No.

I suggest you play 6...c6 insted of 6...e6>>>>>>>>>>>>>>>

Although I've never studied openings, and could be well wrong,I always play this as black against boring E4, and would normally counter Pe6 before moving out the bishop. Opponent usually wastes a move with Pc3 blocking his knight, after that its attack!