Full size image with a link

I’ve gotten my thumbnail to show up on my template, and I can find out how to make it full size, but I’m hoping someone can help me get it to also be a clickable link to the single post page.

Also if I could have it setup to fallback to my original feature image, that would be great. The PHP for Multi Post Thumbnails is different enough from my current theme’s setup that I’m not sure how to blend the 2. I’ve included the existing code in my template that I’d like to integrate my second thumbnail with.

Thanks for any suggestions.

<?php if(has_post_thumbnail()) : ?>
					<?php if(of_get_option('ttrust_post_featured_img_size')=="large") : ?>
		    			<a href="<?php the_permalink() ?>" rel="bookmark" ><?php the_post_thumbnail('otc_large', array('class' => 'postThumb', 'alt' => ''.get_the_title().'', 'title' => ''.get_the_title().'')); ?></a>
					<?php else: ?>
						<a href="<?php the_permalink() ?>" rel="bookmark" ><?php the_post_thumbnail('ttrust_post_thumb_small', array('class' => 'postThumb alignleft', 'alt' => ''.get_the_title().'', 'title' => ''.get_the_title().'')); ?></a>
					<?php endif; ?>
				<?php endif; ?>

http://wordpress.org/plugins/multiple-post-thumbnails/