"We know exactly what to expect. We had the first round in exactly the same environment and we know how difficult it's going to be," said Martinez.
"When a Football League club goes to a non-League environment, I see the non-Leaguers as the favourites.
"Everyone will be looking at it as a potential giant-killing."
It's not easy playing against non-League sides, we saw that in the game between Staines and Stockport," Martinez told the BBC.
"But the squad is looking forward to the challenge. They had a little taste in the first round and everyone looks forward to the magic of the FA Cup.
"Playing against Billericay in the first round was a great help. In football it's impossible to replicate the same environment but that game was a close as we'll get to how it will be in Horsham.
"It'll be difficult to play our usual game - we'll have to adapt to what's required.
"On the other hand, Horsham will treat it as a special day in their history and they'll find strength from where you don't usually find it.
"So we know what to expect but it'll be a fantastic game to be involved in."